1. Field of the Invention
The present invention relates to a solid-state imaging device, a method for driving a solid-state imaging device and a camera system and, in particular, a charge-transfer type solid-state imaging device typically such as a CCD (Charge Coupled Device) imaging device, a driving method therefor and a camera system.
2. Description of the Related Art
In a solid-state imaging device, charges stored in a valid pixel area are taken out as an electric signal from an output section through a vertical transfer section and a horizontal transfer section. Then, the taken electric signal may be recorded to a recording medium for video or may be directly transferred and reproduced on a television deployed on a receiver side, for example.
A technology for a solid-state imaging device adopting the interlace scan-interline transfer (IS-IT) charge transfer method has been proposed that decimates pixels in the vertical direction in order to improve the readout speed (which will be called frame rate).
In an example of the decimation of pixels in a case of the solid state imaging device with a frame rate of 7.5 frame/sec. for outputting all 1280×960 pixels, in order to attain a frame rate of 30 frame/sec., only one of four pixels in the vertical direction is read out, that is, the compression at a compression rate of ¼, which is the rate for reading out pixels is performed on the pixels in the vertical direction for improvement in frame rate.
This method can perform the compression in the vertical direction but does not allow the compression in the horizontal direction. For that reason, when the pixels in the vertical direction of 1280×960 pixels are compressed at the compression rate ¼, 1280×240 pixels are output from an output section. Therefore, it is difficult to keep the aspect ratio for televisions and deteriorate the horizontal to vertical balance. As a result, the necessity occurs for performing the compression in the horizontal direction to keep the aspect ratio 4:3, and the necessity occurs for performing downstream processing for performing the compression in the horizontal direction at the compression rate ¼.
On the other hand, a technology has been proposed that performs compression in the horizontal direction in a horizontal transfer section by handling adjacent two or more predetermined number of vertical transfer sections as one group, establishing correspondence between the group and a unit transfer bit of a horizontal transfer section and transferring charges from a vertical transfer section to the unit transfer bit (which will be called corresponding unit transfer bit, hereinafter) of the horizontal transfer section corresponding to the group to which the vertical transfer section belongs (refer to JP-A-2002-112122 (Patent Document 1), for example).